Tape position sensor, optical

ABSTRACT

An indicating arrangement includes a plurality of tape display systems each including a longitudinally movable display tape having a functional scale and a coded pattern in pre-determined relation thereon. Optical detection units produce digital output signals representative of the actual position of the coded pattern on the tape. An input register produces digital input signals representative of the required position of the coded pattern on the tape. Movement of the tape is controlled by servopositioning means that respond to the digital input and output signals and a central processor is connected to actuate the tape display systems in a time-sharing sequence.

I United States Patent 3,699,421 Stempler et al. 1 Oct. 17, 1972 [54]TAPE POSITION SENSOR, OPTICAL 3,558,895 1/ 1971 Hartman ..250/220 R [72]Inventors: Samuel Stempler, Brooklyn; Jacob I Tellerman, Bayside, bothof NY. Bummer-Benjamin Dobeck Attorney-E. Manning Giles, J. PatrickCagney, Asslgneel Kollslmm lnsmlmem 'l Michael A. Kondzella and RichardA. Zachar Syosset, NY.

22 Filed: Jan. 21, 1971 [571 ABSTRACT [21] APPL 108,460 An indicatingarrangement includes a plurality of tape display systems each includinga longitudinally movable display tape having a functional scale and acoded [52] U.S.Cl. ..318/640, 318/480, 318/562, pattern in predeterminedrelation thereon. optical 250/2 D detection units produce digital outputsignals [51] Ill. Cl. 1/06 representative of the actual p i i of thecoded P [581 of searchmmslmo 250/2190D tern on the tape. An inputregister produces digital 250/22 R input signals representative of therequired position of the coded pattern on the tape. Movement of the tape[56] References cued is controlled by servo-positioning means thatrespond UNITED STATES PATENTS to the digital input and output signalsand a central processor is connected to actuate the tape display3,020,460 2/1962 Morin et al. ..318/480 X systems in a time sharingSequence 3,356,918 12/1967 Williams ..318/162 X 3,358,202 12/1967 Pabstet al. ..318/480 X 11 Claims, 9 Drawing Figures TAPE I SENSOR F T ISWITCH L7 I PuLsE PULSE PULSE i AMPLIFIER AMPLIFIER AMPLIFIER INPUTSCENTRAL L SYNCHRONIZING L PuLsE GENERATOR w INPUT iEF SELEIJION swIT*EF- i0 INPUT REGISTRATION BBL.

MoToR 1 MoToR 2i MoToR it MoToR it [4 3o AMPLIFIER AMPLIFIER AMPLIFIERAMPLIFIER PHOTODETECTOR UNIT I l l DIGITAL To 0 To A 0 TO A 0 TO AANALOG coNvERTER coNvERTER CONVERTER I REG'STER CONVERTER 22 1 SUBTRACWR9 r ERROR a ERROR ERROR g; ERROR 2.

SERVO REGISTER REGISTER REGISTER REGISTER SELECTION SWITCH 2 PATENTEDucI11 I972 SHEET 2 0F 3 PULSE AMPLIFIER TO PHOTODETECTORS "FIG.4

INVENTORS JACOB TELLERMAN 0) SAMUEL .STEMPLER ATTORNEY PAIENTEDMH IHR3.s99;421

SHEEIBBFB CHANNEL I TO & PHOTO- INFRARED RADIAT- ING INPUT PULSE w TAPEINVENTORS JACOB TELLERMAN SAMUEL STEMPLER ATTORNEY DETECTOR BACKGROUNDOF THE INVENTION The present invention relates generally to positionalsensing mechanisms and, more particularly, to an optical sensingarrangement having particular application as a tape position feed-backcomponent in digital computer controlled aircraft instrumentation.

Numerous display units, such as vertical scale aircraft instruments,employ movable display or read-out tapes which are mechanicallypositioned. In the case of vertical scale aircraft instruments forindicating altitude, mach, air speed and the like, air data computerssupply digital input signals to servo drive systems to control thepositioning of the tapes.

Full utilization of the accuracy provided by the digital input signalsdepends upon a concomitant, reliable, accurate and simple tape positionfeed-back unit. Prior instrument systems have used synchros, linear andnon-linear otentiometers, and shaft encoders; all geared to the tapetransport mechanism to monitor and provide the necessary servo errorsignals to control the tape position. These components, while adequatewhen used with analogue input signals, tend to degrade the accuracy thatcan be achieved with an all digital system. Moreover, problems relatedto accuracy, tape stretch, indexing and possible slippage between thefeed-back element and tape, and non-linear display requirements have notbeen entirely negated by existing feed-back components.

SUMMARY OF INVENTION In accordance with the present invention in itsbroad aspect, a highly accurate technique, based upon encoding on therear of each tape the digital equivalent of the data printed on thefront (display) side of the tape, is used to reliably and economicallynegate the problems above mentioned.

The encoding technique, in accordance with a more particular aspect ofthe invention, utilizes a separate optical sensing arrangement for eachtape including a pulse excited emitter of radiant energy, for example,an infrared diode emitter, with a common detector being provided formonitoring the various tapes. An input set of fiber optic bundles, onefor each tape, is positioned to direct multiple components of theemitted radiant energy toward each tape to be incident upon a multitrackpositional code pattern on each tape. A pick-up set of fiber opticbundles, one for each tape, is positioned in close proximity to the codepattern on each tape to pick-up code-affected radiant energy andtransmit such to the detector. The plurality of tapes are seriallyencoded and a central processor is connected to actuate the tape displaysystems on a time-sharing sequence. This permits the use of a commonphoto-detector to respond to the radiant energy transmitted bycorresponding pick-up bundles from each tape. The detector providesposition signals from each tape to be compared to the input signals fromthe air data computer so that a correction signal can be applied to eachservo drive mechanism, one for each tape, to position each tape.

In one embodiment the code pattern on each tape is defined by lighttransmitting and light blocking areas on the tape and the tape isinterposed between the emitter bundles and the pick-up bundles. In thisembodiment infrared light is emitted and the tape, which utilizes a basestrip of a high temperature polyimide, is

covered by a photo emulsion that is exposed photographically so as todefine a code pattern, the tape areas with no coating thereby beingtransparent to infrared transmission.

In another embodiment encoding is accomplished through reflection ofemitted radiant energy from a metalic coating formed in the pattern of areflective Gray binary code on an absorbing black material of the tape,the emitting and the pick-up bundles being positioned on the same sideof the tape.

In each case and in accordance with a more particular, but important,aspect of the invention, the emitting fiber optic bundles are randomlyspliced at their radiant energy input ends, the radiant energy beingsupplied by a number of light emitting diodes so that the radiant energyof each diode is picked-up by at least some of the fibers of eachbundle. This redundancy insuresoperativeness of the systemnotwithstanding failure of one of the emitting diodes. The pick-upbundles are randomly spliced at their output ends to insure a uniformresponse of the common photodetector.

Other features and advantages of the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawings which show structure embodying preferred features of thepresent invention and the principles thereof, and what is now consideredto be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings forming apart of the specification, and in which like numerals are employed todesignate like parts throughout the same:

FIG. 1 is a simplified schematic diagram showing an indicatingarrangement operative in a time-sharing sequence in accordance with thepresent invention;

FIGS. 2 and 3 are detailed views showing the illuminating and detectingtape heads of the monitoring unit;

FIG. 4 is a detailed view showing the front surface of the tape andillustrating numerical readout data thereon;

FIG. 5 is an electrical circuit diagram illustrating a typical pulsedrive circuit;

FIG. 6 is a detailed view illustrating the fiber optic junction of thepick-up bundles and the termination of a separate vertically movabledisplay tape T-l, T-2, T-3

and T-4, each positioned by a separate servo drive system S-1, 8-2, 8-3and 8-4, respectively, in a timeshared'control arrangement in which acommon digital data processor network acts in sequence to comparedigital input signals for each tape with optically derived digitaloutput signals from each tape to provide separate correction signals forappropriately actuating each servo. Typically, air data computers supplydigital input signals representative of altitude, vertical velocity, airspeed, mach, acceleration, angle of attach and the like, each to controla separate display tape. While only four display tapes are shown, itwill e understood that the system may incorporate any desired number inaccordance with the particular display functions to be provided.

In accordance with this invention, each display tape, as shown in FIGS.3 and 4, has display indicia defining a scale 8 on its front facearranged in predetermined relation with a digitally encoded multi-trackpattern P on its back face, the code pattern cooperating with an opticalmonitoring unit M for direct reading of tape position, thereby achievingimproved system accuracy and reliability.

The separate tape control and optical monitoring units are combined in aunique time-sharing system wherein pulsed radiant energy is used toprovide a digital readout of actual tape position for comparison withthe command position fed in binary form.

Each of the servo systems drives a separate tape transport unit, each ofwhich includes a drive roller 10 and one or more idler rollers 11defining a tape travel path that traverses a viewing or window region Wspaced from the locations of the optical monitoring systems.

To derive the digital output signals that represent the actual tapeposition, each optical monitoring unit illustrated in FIG. 1 utilizesinfrared energy in a throughtransmission relation to the tape andincludes a light emitter unit 12 and a detector head 13 disposed inconfronting relation on opposite sides of each tape at a location spacedfrom the viewing window W. The detector heads 13 connect to a commonphoto-detector unit 14 which, as will be explained more fully below, hasa separate detector channel corresponding to each code track, eachdetector channel being supplied from all of the detector heads 13. Solidstate components are used for the emitters and detectors of the infraredenergy to afford reliable operation over a wide temperature range. Aswill become apparent, the optical tape detection system disclosed hereinenables wide utilization of fiber optics to enhance the systemreliability. (Glass fiber wave guides are efficient in transfer ofinfrared light energy, even in various complex bending and twistingconfigurations as may be required.) To provide the digital input signalsthat represent the desired or command position, a set of input registers15-1, 15-2, 15-3 and 15-4, respectively, is provided to store the inputdata as received from an air data computer or other source.

The central processor network includes a central synchronizing pulsegenerator 16 for controlling the time-sharing operation of the systemthrough connection to a tape solid state selector switch 17, a tapeoutput register 18, and a subtract unit 19, in order to monitor eachtape display system separately and in sequence. The tape selectionswitch 17 is connected through a separate pulse amplifier to theindividual light emitter units 12 to provide optical pulsing of thetapes in sequence.

When the first tape T-] is being pulsed, its output is detected in thecommon photodetector unit 14 and transferred to the tape output register18 which presents digital output signals representing actual tapeposition for comparison with digital input signals in input register15-1 to produce a control signal for servo system S-l. Input selectionis provided by the input selection switch 20 (solid state) which issynchronized with pulse generator 16. The succeeding tapes are similarlymonitored, each in sequence and corresponding control signals arederived and applied to each servo system. A solid state servo selectionswitch 21 synchronized by generator 16 gates the subtractor 19 output tothe proper servo.

Each servo system is comprised of a digital error recycle to provide acontinuous analogue control signal for each servo motor.

INFRARED EMITTERS With reference to FIGS. 2 and 3, each light emitterunit 12 consists of an illuminator head 12A that receives a number offiber optic bundles B and an emitter face 128 which mounts four galliumarsenide light emitter diodes 28. Each of the bundles B comprisenumerous individual fibers which are randomly spliced together with theindividual fibers of the other bundles B (see FIG. 2) so that a commonfiber optic bundle B is formed to receive the radiant energy emitted bydiodes 28. This insures that at least some of the individual fibers ofeach of the bundles B receives radiant energy from each of the diodes28. Deterioration of output of one or more diodes produces, therefore,only a minor change in radiant energy applied to any one of the fiberoptic bundles. Even loss of radiant energy from a shorted diode does notaffect the energy output of any bundle greatly because of thesuperimposition and integration effects. Only slight local illuminationchanges will result at the optic fiber bundle output ends.

A pulsed drive circuit is shown in FIG. 5 with its output connectedessentially as a current driver to pulseexcite the four emitter diodes28 which are connected in series. Each diode is excited with a peakcurrent of about 500 milliamperes resulting in a voltage drop of about1.5 volts across each diode. The current level is controlled by theresistor in series with the emitter diodes and the voltage drops of theemitter diodes in the collector circuit of the output transistor.Pulsingtype excitation is utilized to be compatible with or synchronizedby the time-sharing control of the tapes and it is particularlypractical because of the fast response characteristic of the emitterdiodes and because pulsing helps to reduce dissipated power and infrareddiode junction temperature rise.

The light emitter arrangement thus permits an efficient utilization ofinfrared energy, while also providing a high degree of reliabilitythrough redundancy. A shorted diode will not affect the excitation ofother diodes connected in a series in a given pulse circuit. When anemitter diode fails by opening, the remaining series-connected emitterdiodes will not be affected in the circuit arrangement shown in FIG. 5.Each emitter diode is shunted by a set of three series-connected siliconPN junction diodes. The shunting junction diodes provide a path thatcontinues to carry the current in the event the corresponding emitterdiode opens. Typically, the voltage drop across each set of three PNjunction is approximately two volts, so that the shunting diodes arenormally non-conducting during operation of the emitting diodes.

As shown in FIGS. 2 and 3, the fiber optic bundles B transmit theinfrared light from the diodes 28 toward each of the coded tracks on thetape. In the illustrated embodiment, the code pattern P includes tentracks and is illuminated by ten bundles B, a separate one of thebundles B for each code track. It will be appreciated that as aconsequence of the random splicing referred to above, each code trackreceives equal illumination under any condition of emitter diode lightdistribution. As stated above, the optic fibers are composed of glass(rather than plastic) to obtain good transmission characteristics forthe infrared light and to withstand high temperature limits. The lengthof the optic fiber paths is comparatively short so that the light lossis determined by the quality of the terminations of the bundles, ratherthan the loss of transmission due to bundle length.

INFRARED DETECTORS The photodetector unit 14, as stated above, includesthe same number of photodetector channels as the number of code tracksof the code pattern P, each channel being optically connected with allof the detection heads 13. That is, each of the detector heads 13 alignsa set 30 of ten fiber optic bundles BB corresponding to the ten trackcode P. The sets 30 are merged and regrouped, as indicated at J (seeFIGS, 1 and 6) so that at the photodetector end a new set of ten bundlesBB, each consisting only of fibers associated with a common track of thecode patterns P, are formed. Thus, and with reference to FIG. 6, thebundle BB of each of the sets 30 corresponding to channel 1 of the codepatterns P is optically channeled into one of bundles BB, thosecorresponding to channel 2 into another of the bundles BB, and so onwith the remaining channels of the code patterns P. This multiplexingtechnique reduces the required number of receivers in the photodetectionunit 14 thereby reducing the totality of low level circuitry. It will benoted that the individual fibers of each of the bundles BB correspondingto the same channel are randomly spliced at the junction J to insureuniform response at the photodetector unit 14 for each of theinstruments.

A typical photodetector circuit, as shown in FIG. 7, is arranged so thatthe photo-responsive element is sensitive only to pulses so that anyambient light levels that may be present, being essentially DC, will notbe processed. The photo-detector circuit includes a phototransistorresponsive to infrared input and coupled through a capacitor to atransistor switch circuit. The pulsed excitation technique permitsutilization of AC coupling and minimizes the'effects of dark currentsoccasioned by variations in the phototransistor over the widetemperature range.

DISPLAY TAPES A reflected Gray binery code patternis provided on thetape to eliminate the possibility of ambiguity in the position reading.The technique of encoding on the rear of the tape, the digitalequivalent of the visual display data printed on the front of the tape,permits any non-linear tape display function to be easily encoded andeliminates error such as could occur due to slippage in shafts orcouplings.

The display tapes for use with the infrared transmission techniqueemployed in the illustrated embodiment of FIGS. 1 to 7 utilizes a basestrip of a high temperature polyimide, such as is marketed by DuPontunder the trademark KAPTON. The IR transmission (0.92 micron) for astrip of Kapton of .002 inches thickness is approximately 95 percent. Todefine the Gray code pattern of the tape, and the rear face is coveredby a photoemulsion and exposed photographically so that the tape areaswith no coding are transparent to IR transmission. Typically, a trackwidth of 0.040 inches and a sensing window of 0.04 inches X 0.025 inchesis employed.

The front face of the base strip is provided with white coatings todefine the indicia and is provided with a black coating covering theremaining surface areas. A black nylon may be spray-deposited on thefront face and cured in place to provide good adhesion. Varioustechniques may be employed for processing of the tape. For example, theblack nylon may be photosensitive and applied full surface to the basestrip, so that the numerals can then be photographically masked out. Awhite nylon may then be deposited directly to the Kapton to define theindicia. Alternatively, the Kapton may be coated witha photosensitivematerial and coatings may be deposited to define the numerals. A basestrip as thus fabricated has no black on white or white on black tominimize transmission losses.

The white and black films deposited on the front surface aresufficiently thin to allow transmission of about 15 percent infraredradiation, yet appear opaque black and white when illuminated withvisual radiation from the front and backed up with a black plate.

This tape arrangement provides high contrast to the viewer whileenabling effective transmission of infrared and being substantiallyunaffected by ambient light or variations in the ambient light level.

The above monitoring system utilizes transmission of light through thetape for encoding. A similar overall system can be utilized whereby thecoded track consists of a reflective metallic coating formed in thepattern of a reflective Gray binary code on an absorbing black material.I-Iere, however, the infrared light, as illustrated in FIGS. 8 and 9, isdetected by reflection rather than transmission.

As shown in FIG. 8, radiant energy is directed towards the code track Pthrough a number of fiber optic bundles 31, the reflected radiant energybeing transmitted to the photo-detector unit 14 through a correspondingnumber of fiber optic bundles 32. As best shown in FIG. 9, each of thedetector bundles 32 is randomly spliced with a corresponding of theemitter bundles 31 to insure good optical transmission of the incidentand reflected radiant energy.

The first part of the tape in this reflective system may be fabricatedin any desired way since the code in the rear is completely independentof the front. The rear coding is formed by first applying a metallicfilm and then superimposing an absorbing film in the code patterndesired (such as by photo-emulsion).

Light reflection ratio in the infrared region (9200 Angstroms) of theorder of ten to one may be obtained from the reflective surface (such asaluminum) compared to a black absorbing film. This represents areasonable ratio for a practical system. However, this ratio willdeteriorate with wear and tear on the surface and this system is moresensitive to light level and photodetector and amplifier sensitivitythan the system based on transmission, where a ratio of signal of morethan 100 to 1 between light transmission and opaque regions in the tapemay be obtained.

If the type of construction of the tape described for the transmissivelight system cannot be tolerated, or the tape head must be locateddirectly behind the display then the reflective system may be utilizedto advantage.

Thus, while preferred constructional features of the invention areembodied in the structure illustrated herein, it is to be understoodthat changes and variations may be made by those skilled in the artwithout departing from the spirit and scope of the appended claims.

What is claimed is:

l. A multiple display arrangement comprising a plurality of tapes eachhaving a light selective coded pattern in predetermined lengthwisedistributed relation thereon, a plurality of light emitting means, onefor each tape, each irradiating the coded pattern of the correspondingtape with emitted light, common light detection means for said tapes andresponsive to code selected light radiating from the coded patterns ofsaid tapes to produce output digital signals representative of actualtape position, exciter means sequentially actuating said plurality oflight emitting means in a predetermined time-sequence for producing saidoutput digital signals from said detection means in a corresponding timesequence, a plurality of input registers for providing a plurality ofdigital input signals representative of the required position of thetapes, a plurality of servopositioning means, one for each tape, andmeans operating in synchronism with said exciter means to compare in acorresponding time sequence the digital input signals and the digitaloutput signals derived for each tape to provide a separate controlsignal for actuating each servo-positioning means.

2. A multiple display arrangement in accordance with claim 1 whereineach said coded pattern includes a common number of tracks, said lightdetection means including a separate light detector for each track ofsaid coded pattern, and a plurality of sets of optical pick-up lines,one of said sets for each tape and each set including a separate linefor each track of the corresponding coded pattern, each of said sets ofpick-up lines being interposed between a corresponding one of said tapesand said light detection means to transmit code selected light from eachtrack individually to a separate one of the light detectors.

3. A multiple display arrangement in accordance with claim 2 whereineach of said light emitting means includes a set of optical deliverylines that includes a separate delivery line for each track of saidcoded pattern, each said set of optical delivery lines having outputends individually optically aligned with input ends of the correspondingset of said pick-up lines.

4. A multiple display arrangement in accordance with claim 3 whereineach of the delivery lines comprise a fiber optic bundle, the bundlescomprising each of said sets of optical delivery lines being randomlyspliced together at their input ends, and wherein each of said lightemitting means includes a plurality of light emitting diodes eachpositioned to illuminate the input ends of the corresponding one of saidsets of optical delivery lines.

5. A multiple display arrangement in accordance with claim 3 whereineach said coded pattern is defined by light transmitting and lightblocking areas on the corresponding tape, the output ends of thedelivery lines comprising one of said sets of optical delivery lines andthe input ends of the pick-up lines comprising a corresponding set ofsaid optical pick-up lines being disposed in confronting relation onopposite sides of said tape.

6. A multiple display arrangement in accordance with claim 3 whereinsaid coded pattern is defined by light reflecting and light absorbingareas on said tape, the output ends of the delivery lines comprising oneof said sets of optical delivery lines and the input ends of the pick-uplines comprising a corresponding set of said optical pick-up lines beingdisposed in optically confronting relation on the same side of saidtape.

7. A multiple display arrangement comprising a plurality of tapes eachhaving a light selective multitrack coded pattern in predeterminedlengthwise distributed relation thereon, separate light emitter meansfor each tape for each irradiating the coded pattern of thecorresponding tape with a redundant supply of emitted light, commonlight detection means for said tapes and responsive to code selectedlight radiating from the coded patterns for producing output digitalsignals representative of actual tape position, exciter meanssequentially actuating the emitting means in a predeterminedtime-sequence for producing the digital output signals from saiddetection means in a corresponding time sequence, a plurality of inputregisters for providing a plurality of digital input signalsrepresentative of the required positions of the tapes, a plurality ofservopositioning means, one for each tape, and a means operating insynchronism with said exciter means to compare in a corresponding timesequence the digital input signals and the digital output signalsderived for each tape to provide a separate control signal for actuatingeach servo-positioning means.

8. A multiple display arrangement in accordance with claim 7 whereineach of said emitting means includes a plurality of light emittingdiodes arranged to provide an area of superimposed emitted light and aplurality of optical delivery lines positioned to jointly receive thesuperimposed light and individually deliver components of thesuperimposed light toward one each of the tracks of the correspondingcoded pattern.

9. A multiple display arrangement in accordance with claim 8 wherein thelight emitting diodes of each of said emitting means compriseseries-connected infrared emitting diodes.

10. A multiple display arrangement in accordance with claim 8 andincluding a separate set of series-connected diodes connected in shuntwith each of said 9 light emitting diodes and exhibiting a voltage dropslightly greater than the voltage drop of the corresponding emittingdiode.

l l. A multiple display arrangement comprising a plurality of tapes eachhaving a multi-track coded pattern in predetermined length-wisedistributed relation thereon, each coded pattern consisting of a commonnumber of tracks, a plurality of light emitter means, one for each tape,each of said emitter means including a plurality of light emittingdiodes arranged to provide an area of superimposed emitted light and aplurality of optical delivery lines positioned to jointly receive thesuperimposed light and individually deliver components of thesuperimposed light toward one each of the tracks of the correspondingcoded pattern, common light detection means for said tapes and includinga separate light detector for each track of said multitrack codedpattern, and a separate set of optical pickup lines disposed in lighttransmitting relation with each of said photo detectors, the pick-uplines of each set being disposed in light receiving relation with onetrack each of the coded pattern of all said tapes, exciter meanssequentially actuating said plurality of light emitter means in apredetermined time-sequence for producing digital output signals fromsaid detection means in a corresponding time sequence representing theactual position of each tape, a plurality of input registers forproviding a plurality of digital input signals representative of therequired position of the tapes, a plurality of servo-positioning means,one for each tape, and means operating in synchronism with said excitermeans to compare in a corresponding time sequence the digital inputsignals derived for each tape to provide a separate control signal foractuating each servo-posh tioning means.

1. A multiple display arrangement comprising a plurality of tapes eachhaving a light selective coded pattern in predetermined lengthwisedistributed relation thereon, a plurality of light emitting means, onefor each tape, each irradiating the coded pattern of the correspondingtape with emitted light, common light detection means for said tapes andresponsive to code selected light radiating from the coded patterns ofsaid tapes to produce output digital signals representative of actualtape position, exciter means sequentially actuating said plurality oflight emitting means in a predetermined time-sequence for producing saidoutput digital signals from said detection means in a corresponding timesequence, a plurality of input registers for providing a plurality ofdigital input signals representative of the required position of thetapes, a plurality of servo-positioning means, one for each tape, andmeans operating in synchronism with said exciter means to compare in acorresponding time sequence the digital input signals and the digitaloutput signals derived for each tape to provide a separate controlsignal for actuating each servo-positioning means.
 2. A multiple displayarrangement in accordance with claim 1 wherein each said coded patternincludes a common number of tracks, said light detection means includinga separate light detector for each track of said coded pattern, and aplurality of sets of optical pick-up lines, one of said sets for eachtape and each set including a separate line for each track of thecorresponding coded pattern, each of said sets of pick-up lines beinginterposed between a correspOnding one of said tapes and said lightdetection means to transmit code selected light from each trackindividually to a separate one of the light detectors.
 3. A multipledisplay arrangement in accordance with claim 2 wherein each of saidlight emitting means includes a set of optical delivery lines thatincludes a separate delivery line for each track of said coded pattern,each said set of optical delivery lines having output ends individuallyoptically aligned with input ends of the corresponding set of saidpick-up lines.
 4. A multiple display arrangement in accordance withclaim 3 wherein each of the delivery lines comprise a fiber opticbundle, the bundles comprising each of said sets of optical deliverylines being randomly spliced together at their input ends, and whereineach of said light emitting means includes a plurality of light emittingdiodes each positioned to illuminate the input ends of the correspondingone of said sets of optical delivery lines.
 5. A multiple displayarrangement in accordance with claim 3 wherein each said coded patternis defined by light transmitting and light blocking areas on thecorresponding tape, the output ends of the delivery lines comprising oneof said sets of optical delivery lines and the input ends of the pick-uplines comprising a corresponding set of said optical pick-up lines beingdisposed in confronting relation on opposite sides of said tape.
 6. Amultiple display arrangement in accordance with claim 3 wherein saidcoded pattern is defined by light reflecting and light absorbing areason said tape, the output ends of the delivery lines comprising one ofsaid sets of optical delivery lines and the input ends of the pick-uplines comprising a corresponding set of said optical pick-up lines beingdisposed in optically confronting relation on the same side of saidtape.
 7. A multiple display arrangement comprising a plurality of tapeseach having a light selective multi-track coded pattern in predeterminedlengthwise distributed relation thereon, separate light emitter meansfor each tape for each irradiating the coded pattern of thecorresponding tape with a redundant supply of emitted light, commonlight detection means for said tapes and responsive to code selectedlight radiating from the coded patterns for producing output digitalsignals representative of actual tape position, exciter meanssequentially actuating the emitting means in a predeterminedtime-sequence for producing the digital output signals from saiddetection means in a corresponding time sequence, a plurality of inputregisters for providing a plurality of digital input signalsrepresentative of the required positions of the tapes, a plurality ofservo-positioning means, one for each tape, and a means operating insynchronism with said exciter means to compare in a corresponding timesequence the digital input signals and the digital output signalsderived for each tape to provide a separate control signal for actuatingeach servo-positioning means.
 8. A multiple display arrangement inaccordance with claim 7 wherein each of said emitting means includes aplurality of light emitting diodes arranged to provide an area ofsuperimposed emitted light and a plurality of optical delivery linespositioned to jointly receive the superimposed light and individuallydeliver components of the superimposed light toward one each of thetracks of the corresponding coded pattern.
 9. A multiple displayarrangement in accordance with claim 8 wherein the light emitting diodesof each of said emitting means comprise series-connected infraredemitting diodes.
 10. A multiple display arrangement in accordance withclaim 8 and including a separate set of series-connected diodesconnected in shunt with each of said light emitting diodes andexhibiting a voltage drop slightly greater than the voltage drop of thecorresponding emitting diode.
 11. A multiple display arrangementcomprising a plurality of tapes each having a multi-track coded patternin predetermined length-wise distributed relation thereon, each codedpattern consisting of a common number of tracks, a plurality of lightemitter means, one for each tape, each of said emitter means including aplurality of light emitting diodes arranged to provide an area ofsuperimposed emitted light and a plurality of optical delivery linespositioned to jointly receive the superimposed light and individuallydeliver components of the superimposed light toward one each of thetracks of the corresponding coded pattern, common light detection meansfor said tapes and including a separate light detector for each track ofsaid multi-track coded pattern, and a separate set of optical pick-uplines disposed in light transmitting relation with each of said photodetectors, the pick-up lines of each set being disposed in lightreceiving relation with one track each of the coded pattern of all saidtapes, exciter means sequentially actuating said plurality of lightemitter means in a predetermined time-sequence for producing digitaloutput signals from said detection means in a corresponding timesequence representing the actual position of each tape, a plurality ofinput registers for providing a plurality of digital input signalsrepresentative of the required position of the tapes, a plurality ofservo-positioning means, one for each tape, and means operating insynchronism with said exciter means to compare in a corresponding timesequence the digital input signals derived for each tape to provide aseparate control signal for actuating each servo-positioning means.